Liquid flask



FIG. 1 is a front elevation view of the liquid flask showing my new design;

FIG. 2 is a side elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is an exploded side elevation view thereof.

The bottom view of the liquid flask forms no part of the claimed design. 

The ornamental design for a liquid flask, as shown and described. 